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Sphalerite from
Thomaston Dam railroad cut, Thomaston Dam, Thomaston, Litchfield Co., Connecticut, USA

Classification
Species:Sphalerite
Formation:Primary
Comments:In hydrothermal fault veins associated with barite, calcite, fluorite, galena, pyrite, quartz, and zeolites. Pete Dunn analyzed crystals in 1973: “It has been said that the wurtzite from Thomaston Dam, Connecticut, was of a type that changed to sphalerite under the crushing necessary for a powder x-ray photo. This thought intrigued me and I checked it out by taking a regular powder photo after crushing the sample in the usual fashion, and then took another x-ray using the Gandolfi camera which gives powder photos from single crystals. Result — both photos perfect sphalerite patterns, and identical" (Yedlin, 1973a). Henderson (1979) showed diagrams of sphalerite crystals epitaxial on supposed wurtzite, and the other way around, with a (0001) (pinacoidal) face of "wurtzite" matching a (111) (tetrahedral) face of sphalerite. In any case, the crystals from this locality, commonly labeled "wurtzite" appear to be polysynthetically twinning, combined positive and negative tetrahedra of sphalerite on a 6-sided (111) face. Note the re-entrant angles that circumscribe the "prisms" of these crystals, which are indicative of twinning.
Habit:pagoda-like polysynthetic twins on (111) resulting in pseudo-hexagonal "prisms" with re-entrant striae
Colour:dark reddish-brown, dark brown, black
Quality for species:Excellent - world class for species or very significant. (!!)
Abundance at site:Common
Confirmation
Validity:Confirmed
Confirmation Methods:XRD
References
References:Yedlin, Neal. (1973a), Yedlin on Micromounting. Mineralogical Record: 4(2).; Yedlin, Neal. (1973b), Yedlin on Micromounting. Mineralogical Record: 4(6).; Fluorite: The Collector's Choice. Extra Lapis English No. 9; Segeler, Curt and Molon, Joseph. (1985), The Thomaston Dam Site, Thomaston, Connecticut; Rocks & Minerals: 60(3): 119-124.; Henderson, William A. (1995), Microminerals of Connecticut; Rocks & Minerals: 70: 420-425.; Henderson, William A. (1979), Microminerals. Thomaston Dam. Mineralogical Record: 10: 239-241.; Vogt, Wolfgang. (1991), Rediscovering Thomaston Dam. Lapidary Journal: April.
Associated Minerals Based on Photo Data:
Quartz5 photos of Sphalerite associated with Quartz at this locality.
Pyrite3 photos of Sphalerite associated with Pyrite at this locality.
Heulandite3 photos of Sphalerite associated with Heulandite at this locality.
Data
Mineral Data:Click here to view Sphalerite data
Locality Data:Click here to view Thomaston Dam railroad cut, Thomaston Dam, Thomaston, Litchfield Co., Connecticut, USA
Nearest other occurrences of Sphalerite
7.7km (4.8 miles) A State Route 8 and State Route 118 interchange, Harwinton, Litchfield Co., Connecticut, USA
12.2km (7.6 miles) B Bristol Copper Mine, Bristol, Hartford Co., Connecticut, USA
20.0km (12.4 miles) C Tomasso Quarry (Tilcon Tomasso Quarry; Tilcon Quarry; Arborio Quarry), Farmington, Hartford Co., Connecticut, USA
20.0km (12.4 miles) D Trap Rock quarry, Plainville, Hartford Co., Connecticut, USA
20.1km (12.5 miles) E Canton Lead Mines (Cherry Brook lead mine), Rattlesnake Mountain, Canton, Hartford Co., Connecticut, USA
23.8km (14.8 miles) F O & G Southbury Quarry (Silliman Quarry; O & G No. 2 Quarry), Southbury, New Haven Co., Connecticut, USA
24.8km (15.4 miles) G Kyanite locality (Judds Bridge locality), Washington, Litchfield Co., Connecticut, USA
25.2km (15.6 miles) H State Route 9 - Ellis Street and State Route 72 interchanges (State Route 72 roadcut), New Britain, Hartford Co., Connecticut, USA
25.8km (16.0 miles) I Hart's Lead Mine, Berlin, Hartford Co., Connecticut, USA
26.5km (16.4 miles) J Rockside Quarry (Mine Hill Quarry), Mine Hill (Ore Hill), Roxbury, Litchfield Co., Connecticut, USA
26.8km (16.6 miles) K Roxbury Iron Mine (Shepaug Iron Company Mine; Shepaug Spathic Iron and Steel Company Mine), Mine Hill (Ore Hill), Roxbury, Litchfield Co., Connecticut, USA
28.6km (17.8 miles) L Newington, Hartford Co., Connecticut, USA
30.1km (18.7 miles) M 2368-2384 Berlin Turnpike (Former Hartford Drive-In), Newington, Hartford Co., Connecticut, USA
34.5km (21.4 miles) N Sandy Hook gold mine (Blackwell's mine), Sandy Hook, Newtown, Fairfield Co., Connecticut, USA
37.0km (23.0 miles) O Old lead mine, Brookfield, Fairfield Co., Connecticut, USA
38.1km (23.7 miles) P Roncari Quarry (Tilcon Quarry), East Granby, Hartford Co., Connecticut, USA
38.6km (24.0 miles) Q U. S. Route 7 Expressway (Danbury line to Iron Works District), Brookfield, Fairfield Co., Connecticut, USA
39.6km (24.6 miles) R Andrews Quarry (old Hale Quarry; Grandfather Andrews Quarry), Portland, Middlesex Co., Connecticut, USA
40.7km (25.3 miles) S Pfizer Company Marble Quarry (New England Lime Co. quarry; NELCO quarry; Specialty Minerals Inc.; Minerals Technologies Inc.; Canaan Limestone Quarry; Connecticut Lime Company; Canaan Lime Company; Lewis Quarry), Canaan, North Canaan, Litchfield Co., Connecticut, USA
40.9km (25.4 miles) T Middletown lead mines (Middletown Mine), Middletown, Middlesex Co., Connecticut, USA
41.1km (25.6 miles) U Knob Hill Quarry, Glastonbury, Hartford Co., Connecticut, USA
41.1km (25.6 miles) V State Farm Quarry (Road Metal Quarry), Middletown, Middlesex Co., Connecticut, USA
41.2km (25.6 miles) W Schoonmaker Mine (Cramer Mine), Strickland pegmatite (Strickland-Cramer Quarry; Strickland-Cramer Mine; Strickland-Cramer Feldspar-Mica Quarries), Collins Hill, Portland, Middlesex Co., Connecticut, USA
41.3km (25.6 miles) X Strickland Quarry (Eureka Quarry), Strickland pegmatite (Strickland-Cramer Quarry; Strickland-Cramer Mine; Strickland-Cramer Feldspar-Mica Quarries), Collins Hill, Portland, Middlesex Co., Connecticut, USA
42.0km (26.1 miles) Y Booth's Mine (Booth's Bismuth Mine; Booth-Hurd's Bismuth Mine), Monroe, Fairfield Co., Connecticut, USA
42.0km (26.1 miles) Z White Rocks Quarry (Consolidated Quarry), White Rock District (White Rocks District), Middletown, Middlesex Co., Connecticut, USA
42.2km (26.2 miles) 0 Tollgate Quarry (Tollgate Mine; Bidwell Quarry; China-stone Quarry), Middletown, Middlesex Co., Connecticut, USA
42.3km (26.3 miles) 1 Paxton Way, Glastonbury, Hartford Co., Connecticut, USA
42.5km (26.4 miles) 2 Canaan, North Canaan, Litchfield Co., Connecticut, USA
42.7km (26.5 miles) 3 Lane's Mine (Lane's Lead and Silver Mine; Elm Street), Monroe, Fairfield Co., Connecticut, USA
43.5km (27.0 miles) 4 East Rock, New Haven, New Haven Co., Connecticut, USA
45.0km (28.0 miles) 5 State Forest Quarry #2 (State Forest No. 2 Mica Mine), Cobalt, East Hampton (Chatham), Middlesex Co., Connecticut, USA
45.1km (28.0 miles) 6 Great Hill cobalt mines, Cobalt, East Hampton (Chatham), Middlesex Co., Connecticut, USA
45.3km (28.1 miles) 7 North Street mall, Danbury, Fairfield Co., Connecticut, USA
46.6km (29.0 miles) 8 State Route 22 roadcut, Millerton, North East Township (Northeast), Salisbury District, Dutchess Co., New York, USA
47.2km (29.3 miles) 9 Old Mine Plaza construction site, Long Hill, Trumbull, Fairfield Co., Connecticut, USA
Mineral and/or Locality  
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